The present invention relates to an illuminator for use as a back light of liquid crystal display (LCD) and an LCD device using the illuminator. More specifically, the invention relates to an illuminator of a simplified structure which provides a high lighting efficiency, and to an LCD device using the illuminator.
The LCDs have been widely used in personal computers, word processors, VCR cameras, etc. as image display means. Field of the application is expected to further expand and diversified.
FIG. 15 shows a widely-used conventional LCD device. Referring to FIG. 15, a light guide 51 is provided with a light diffusion face 52, which diffusion face comprising a plurality of dot patterns printed with white ink on the bottom surface or a plurality of protrusions provided on the diffusion face. A light source 53 is formed of a cold-cathode fluorescent tube, for example. A light reflector 54 reflects the light generated from the cold-cathode fluorescent tube. A reflector sheet 55 is provided on the bottom surface, and a light diffusion plate 56 is provided close to the upper surface of the light guide 51. A prism sheet 57 is provided on the light diffusion plate 56. An LCD element 7 is provided on the upper surface of the prism sheet 57.
When the light source 53 is lit, both the direct light and the light reflected by the reflector 54 are delivered to the light guide 51 and the incident light propagates in the light guide 51, and diffused by the light diffusion face 52 to be sent out of the light guide 51. The light sent out from the bottom surface of the light guide 51 is reflected by the reflector sheet 55 to be returned again into the light guide 51, which light is ultimately emitted from the upper surface of the light guide 51.
The light discharged from the upper surface of the light guide 51 is diffused by the light diffusion plate 56, which blinds, for example, the dot patterns. The light diffused by the light diffusion plate 56 is regulated by the prism sheet 57 to the direction towards front for illuminating the LCD element 7 from the behind. When the LCD element 7 is driven by a driving circuit (not shown), the display device exhibits images to be recognized by the eyes.
Another example of the conventional illuminators (not shown) comprises a light guide of a rectangular parallelepiped shape, where the upper surface is substantially parallel to the bottom surface. The rest of the sections being structured similar to the conventional illuminators.
There are a number of problems with the conventional illuminators. For example, the light diffusion face 52, the reflector sheet 55, disposed on the bottom surface of the light guide 51, as well as the light diffusion plate 56, the prism sheet 57, disposed on the upper surface of the light guide 51 deteriorate impair the light efficiency by the absorption.
The conventional illuminators employ a number of sheets, such as the light reflector sheet 55 which is disposed on the bottom surface of the light guide 51, the light diffusion plate 56 and the prism sheet 57 disposed on the upper surface of the light guide 51, each of these sheets needs to be aligned properly to a predetermined location. Also, there are possibilities that unwanted foreign items coming in between the sheets to a deteriorated quality. All these are the factors that push up the manufacturing cost. In order to improve the above-described drawbacks, it has been requested to reduce the number of such sheets.
Another problem pertinent to the conventional LCD devices is the so-called viewing angle; namely, when an LCD screen is viewed off the central angle it turns out difficult to clearly recognize a displayed image. The recently introduced LCDs have the viewing angle 140xc2x0, 160xc2x0, etc., yet they are not yet reaching a satisfactory level.
An illuminator of simplified structure and uniform luminance for use in the LCD devices has been proposed in the Japanese Laid-open Patent No. 10-197723. It is asserted that the illuminator provides an improved luminance, and eliminates the prism sheet as well as the diffusion sheet. A light guide of the illuminator is provided in the bottom surface with a group of mirror-surfaced microscopic asperities consisting of a triangular shape, extending in parallel to a linear light tube. It is taught that at least one item among the gap in the group of the microscopic asperities, the depth of a groove and the angle of a slope inclination is varied from one side face, at which the light is taken in, towards the other side face of the light guide; the height and the depth are made to be greater, the space between the groups to be narrower towards the other side face of the light guide.
The above laid-open patent describes that it produces a uniform luminance by providing variations in the group of microscopic asperities. However, it does not teach us any practical means how the uniform luminance is actually implemented. In practice, it is difficult to produce the uniform luminance in accordance with the disclosed description, providing a variation in the height, in the depth and in the space among the group of microscopic asperities. In order to produce an increased luminance and make it uniform, it is essential to specify the interrelationship among the height, the space of the asperities with the light guide.
The present invention addresses the above points and proposes practical means for implementing an actual illuminator with which the drawbacks in the viewing angle are improved through an improved efficiency of light utilization, and the prism sheet is eliminated. The present invention also contains an LCD device using the above-described illuminator.
A first illuminator of the present invention comprises a light guide whose upper surface is horizontal while the bottom surface is slanting to the upper surface. A light source is provided at a side face having greater thickness of a light guide. A light diffusion plate is provided on the upper surface of the light guide, and a reflector sheet is provided on the bottom surface. The light guide is provided in the bottom surface with a plurality of groove groups extending parallel to the above-described side face, and a flat face bridging the groove groups. The plurality of groove groups are formed so that the depth of a constituent groove in each of the groove groups gradually increases along with an increasing distance departing from the above-described side face, and the pitch in terms of a sum of the width of a groove group and the width of a flat face bridging the groove groups remains constant throughout a distance from the above-described side face to the other side face of a light guide.
A second illuminator of the present invention uses a light guide whose shape is identical to two pieces of the light guide of the above first illuminator jointed together at the middle in the respective side faces of smaller thickness. A light source is provided at both of the side faces of greater thickness opposing to each other. A reflector sheet is provided along the bottom surface of a light guide. The light guide is provided on the upper surface a light diffusion plate, and in each of the respective bottom surface sections formed from the respective side faces towards the middle, with the same pluralities of the groove groups and the flat faces bridging the groove groups as provided in the bottom surface of the above first light guide.
A third illuminator of the present invention comprises a light guide whose upper surface and the bottom surface are parallel to each other, a light source provided at one side face of a light guide, a reflector sheet provided on the bottom surface of the light guide and a light diffusion plate provided on the upper surface of the light guide. The light guide is provided in the bottom surface with a plurality of groove groups extending parallel to the above-described side face, and a flat face bridging the groove groups. The plurality of groove groups are formed so that the depth of a constituent groove in each of the groove groups gradually increases along with an increasing distance departing from the above-described side face, while the pitch in terms of a sum of the width of a groove group and the width of a flat face bridging the groove groups is fixed constant throughout a distance from the above-described side face to the other side face of a light guide.
A fourth illuminator of the present invention comprises a light guide whose upper surface is horizontal while the bottom surface is slanting to the upper surface. A light source is provided at a side face having a greater thickness of a light guide. The light guide is provided on the upper surface with a light diffusion plate, and on the bottom surface with a reflector sheet. The light guide is provided in the bottom surface with a plurality of groove groups extending in parallel to the avove-described side face, and a flat face bridging the groove groups. The depth of a constituent groove in each of the groove groups is fixed at a certain value in a region from the above-described side face to the proximity area, and then it is gradually increased along with a distance from the proximity area towards the other side face; while the pitch in terms of a sum of the width of a groove group and the width of a flat face bridging the groove groups is gradually decreased from the above-described side face towards the proximity area, and then it is fixed constant in a region from the proximity area to the other side face.
A fifth illuminator of the present invention comprises a light guide whose shape is identical to two pieces of the light guide used in the fourth illuminator, jointed together at the middle in the respective side faces of smaller thickness. A light source is provided at both of the side faces of greater thickness opposing to each other. The light guide is provided on the bottom surface with a reflector sheet, and on the upper surface with a light diffusion plate. The light guide is provided in each of the respective bottom surface sections formed from the respective side faces towards the middle with the same pluralities of the groove groups and the flat faces bridging the groove groups as provided in the bottom surface of the fourth light guide.
A sixth illuminator of the present invention comprises a light guide whose upper surface and the bottom surface are parallel to each other, a light source provided at one side face of a light guide, a reflector sheet provided on the bottom surface of the light guide and a light diffusion plate provided on the upper surface of the light guide. The light guide is provided in the bottom surface with a plurality of groove groups extending in parallel to the above-described side face, and a flat face bridging the groove groups. The depth of a constituent groove in each of the groove groups is fixed at a certain value in a region from the above-described side face to the proximity area, and then it is gradually increased along with a distance departing from the proximity area towards the other side face; while the pitch in terms of a sum of the width of a groove group and the width of a flat face bridging the groove groups is gradually decreased from the above-described side face towards the proximity area, and then it is fixed constant in a region from the proximity area to the other side face.
A seventh illuminator of the present invention comprises either one of the above light guides recited in the first through sixth inventions, which light guide is further provided in the upper surface with a plurality of ditches extending perpendicular to the side face of the light guide.
An eighth item of the present invention is an LCD device that comprises either one of the above illuminators described in the first through seventh inventions provided on the light diffusion plate with an LCD element.